This invention relates to an image forming apparatus provided with a document table movable reciprocatingly to the left and right along a lengthwise direction thereof, and thereby a document placed on the document table is exposed.
Copying machines or like image forming apparatus are categorized into two types in the light of document exposing method: one is an image forming apparatus provided with a movable optical system; and the other is an image forming apparatus provided with a movable document table. In these apparatus, the optical system or document table moves horizontally to expose a document. In the image forming apparatus provided with a movable document table, when a copying operation is instructed after a document is set in the document table, the document table moves in a specified direction from a home position so as to expose the document. Upon completion of exposure of the document, the document table is returned to the home position, whereupon a movement control of the document table is released and the document table is allowed to make free movement.
Recently, there has been an increasing demand for an image forming apparatus which can be readily and easily used at home. In order to meet this demand, the image forming apparatus requires to be manufactured small-sized, light-weighted, and at lower costs. In this aspect, the image forming apparatus provided with a movable document table is more suitable for home use than the one provided with a movable optical system.
In the image forming apparatus provided with a movable document table, it is required that movement of the document table to the left and right be controlled. In a conventional large-sized apparatus of this type, sensor switches are provided in specified positions on the left and right side portions of the apparatus. It is detected in accordance with ON and OFF sensor signals from the sensor switches that the document table has reached the left or right specified position, and then a moving direction of the document table is reversed with the use of an electromagnetic spring clutch. In other words, the movement of the document table is controlled electrically. However, the electric control requires at least a sensor switch and electromagnetic spring clutch. These parts, being expensive, cause an increase in manufacturing cost of the image forming apparatus. Further, these electric parts require wiring for connecting them, which necessarily increases the manufacturing cost. Accordingly, in manufacturing a low cost image forming apparatus for home use, it is not suitable to control movement of the document table electrically.
If an image forming apparatus provided with a movable document table is manufactured small-sized and light-weighted, an installation place thereof can be readily changed and a main body thereof can be easily inclined in case of, for example, removing a jammed copy sheet. However, it is necessary to prevent the document table from moving freely in the case where the installation place of the apparatus is changed or the main body thereof is inclined. If the document table is allowed to move freely with the inclination of the apparatus main body, the unexpectedly moved document table may break the apparatus or hurt an operator.
Moreover, it is preferable to stop the document table in a center position of the image forming apparatus since the document table can be stably and reliably supported on the apparatus main body. However, in this case, the document table is more liable to move to the left and right. Accordingly, it is even more necessary to prevent the document table from moving freely. An electric control may be executed so as to lock the document table in a predetermined position. However, as described above, the use of electric parts necessarily causes an increase in manufacturing cost.
In addition, the document table should be stopped in the predetermined position upon completion of the copying operation. It is exceedingly difficult to stop the document table in the predetermined position only by stopping a drive motor for moving the document table. In consideration of the inertia of the document table in motion, a very complicated calculation should be carried out to obtain a stop timing of the drive motor so as to stop the document table in the predetermined position. However, a microcomputer capable of performing complicated calculations cannot be provided in the image forming apparatus for home use which requires to be manufactured at a reduced cost. Therefore, it is necessary to provide stop means for stopping the document table in the predetermined position which is simple in construction and manufactured at low costs.
In view of the above problems, it is an object of the present invention to provide an image forming apparatus provided with a movable document table which is simple in construction and manufactured at low costs.